1. Field of the Invention
The present invention relates to a video signal processing method and an apparatus therefor, and more specifically, it relates to a video signal processing method and an apparatus therefor for a picture-in-picture function of inserting a small screen in a part of a television screen.
2. Description of the Prior Art
Technique of inserting a plurality of small subscreens in a main screen of a television receiver is well known in the name of picture-in-picture function Such a picture-in-picture function is basically achieved by temporarily writing the contents of the subscreen in a field memory thereby to read the same in a position to be displayed along scanning of the main screen.
In general, the signal for the main screen is not synchronized with the signal for the subscreen, whereby correct color processing cannot be performed when the signal for the subscreen is directly written in the memory in the form of a composite color television signal (i.e., NTSC signal). In a conventional video signal processing method for the picture-in-picture function, therefore, the composite color television signal has been separated into a luminance signal and color difference signals to be respectively written in corresponding field memories, thereby to read the same synchronously with the main screen in a time-base compressed manner, for obtaining a video signal corresponding to the reduced subscreen. Such a video signal processing method is disclosed in, for example, "Television Gijutsu", Japanese Periodical, December 1984, pp. 31-37.
In such a conventional video signal processing method, however, the composite color television signal must be separated into a luminance signal Y and color difference signals R-Y and B-Y to be written in the corresponding field memories, whereby the circuit structure is complicated and large memory capacity is required.